The present invention relates generally to a novel gerotor pump having an eccentric ring housing with an integral pressure chamber for a motor vehicle hydraulic differential. More particularly, the present invention relates to a new eccentric ring housing with an integral pressure chamber for a gerotor pump used in a motor vehicle hydraulic differential which is particularly suitable for use in hydraulic limited slip differentials for axles, transfer case center differentials and similar devices.
Gerotor pumps are generally well known and are commonly used in numerous motor vehicle drivetrain subassemblies. In general, gerotor pumps include three (3) main components, an inner rotor, an outer rotor and an eccentric ring. The inner rotor preferably has one less tooth than the outer rotor and has a center line positioned at a fixed eccentricity from the center line of the outer rotor. Conjugately generated tooth profiles maintain substantially continuous fluid-tight contact between the inner rotor and the outer rotor during operation of the gerotor pump. As the inner rotor rotates, liquid is drawn into an enlarging chamber formed by the missing tooth in the inner rotor to a maximum volume which is equal to that of the missing tooth in the inner rotor. Liquid is then forced out of the chamber as the teeth of the inner rotor and the rotor housing again mesh, thereby decreasing the volume of the chamber. In certain applications, the gerotor pump may be configured such that the outer rotor is connected to rotate with a first shaft and the inner rotor is connected to rotate with a second shaft. In such a configuration, no fluid is displaced by the gerotor pump unless the first shaft and the second shaft are rotating at different speeds relative to each other, thereby causing differential rotation of the inner rotor and the outer rotor relative to each other.
One common application of gerotor pumps in motor vehicle drivetrain subassemblies involves utilizing the gerotor pump to provide fluid pressure to actuate a clutch assembly in response to differential rotation between rotating members. Gerotor pumps may also be used in motor vehicle drivetrain subassemblies to circulate lubricating fluid to the various components in the motor vehicle drivetrain assembly. Gerotor pumps generally include an inlet port and an outlet port which are positioned approximately 180 degrees apart. When non-reversing gerotor pumps are utilized, a change in the direction of rotation of the inner rotor relative to the outer rotor causes a reversal in the direction of flow of fluid from the outlet port to the input port. In many motor vehicle applications, it is desirable to use a reversing gerotor pump such that reversal in the relative direction of rotation between the inner rotor and the outer rotor does not cause a corresponding reversal in the direction of fluid flow from the inlet port to the outlet port. This is generally accomplished by positioning the outer rotor within a free-turning eccentric ring. A stop pin is also generally provided to limit rotation of the eccentric ring to 180 degrees in either direction. Changing the eccentricity of a gerotor pump by allowing the eccentric ring to rotate 180 degrees also reverses the direction of fluid flow. Therefore, if upon a reversal of the relative direction of rotation between the inner rotor and the outer rotor in the gerotor pump, the eccentric ring is caused to rotate 180 degrees, the direction of fluid flow will remain unchanged, from the inlet port to the outlet port. In motor vehicle drivetrain subassemblies and other applications involving frequent reversals of a gerotor pump, the reversals will often cause excessive wear on the gerotor pump. Other methods have been developed for unidirectional fluid flow for non-reversible gerotor pumps such as commutators or special valve arrangements.
In applications where the gerotor pump is utilized to provide fluid pressure to actuate a clutch assembly in response to differential rotation between rotating members, a piston housing is typically placed adjacent to the gerotor pump assembly. The piston housing is typically configured with a piston inlet passage, which is generally an aperture through the wall of the piston housing, allowing fluid to enter the piston housing and force a piston against a clutch pack or typical clutch assembly. Problems with this type of arrangement include using additional parts, potential fluid leakage (pressure loss) at the mating register surfaces of the gerotor pump and the piston housing, as well as additional friction forces between the outer rotor and the piston housing such as with reversible gerotor pumps. In addition, these prior art gerotor pumps typically require some type of pressure relief system external to the gerotor pump.
The present invention provides the advantage of combining the eccentric ring, the piston housing, and the gerotor pump pressure relief system all in one unit. This allows the advantage of less parts, less pressure loss due to fluid leakage, less wear between gerotor components and the piston housing, and the need for external pressure relief systems. These and other advantages of the present invention are provided by a gerotor pump comprising an inner rotor having a plurality of external teeth, an outer rotor having a plurality of internal teeth, and a one piece eccentric ring housing. The one piece eccentric ring housing has a first side opposite a second side and an aperture extending therethrough. The first side comprises an eccentric ring formed by an eccentrically positioned recess for housing the inner rotor and outer rotor. The second side comprises an annular recess forming a piston housing.